Document-level keydown handler covers the W3C tree-view pattern so
users can drive the browse pane without the mouse:
↓ / ↑ — move selection (auto-previews files as the cursor
lands so the right pane keeps up)
→ — expand collapsed folder; jump to first child if
already expanded; no-op on leaves
← — collapse expanded folder; otherwise jump to parent
Enter / Space — preview file / toggle folder
Home / End — first / last visible row
Bails out cleanly when focus is in an input/textarea/contenteditable
or when a modal / context menu is open, so it doesn't fight existing
filter typing, YAML editor, or the right-click menu's own keys. Any
modifier (Ctrl/Cmd/Alt) lets the browser shortcut through unchanged.
Selection updates scroll the now-current row into view via
scrollIntoView({block:'nearest'}). Tree module gains a visibleIds
export so events.js can walk the same filtered+expanded order the
renderer uses.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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